1. Field of the Invention
This invention relates to water-resistant, corrugated cardboard. Such corrugated cardboard, for example, can be utilized for all-weather pallets and containers.
2. Discussion of the Related Art
Most pallets used for transportation, carriage or the like in various places such as factories, airports and/or seaports are conventionally made of wood, and some are made of plastic or steel. However, there have been such problems, as follows, if they are made of any such materials.
Because pallets are usually transported to the destination together with loads placed on them, they are frequently brought into foreign countries. In such a case, some countries require that the wooden pallets be quarantined by fumigation or the like, just like imported animals and plants. Such quarantine periods, which usually take a considerable length of time, often cause problems for trading, which requires quick action.
It is therefore conceivable to use pallets made of plastic or steel. However, the former causes problems in disposal. The latter substantially raises the freight cost, especially if the goods to be loaded are rather light, since the shape and size of the pallet necessary for use make the pallet considerably heavy.
Taking the aforementioned matters into consideration, the pallets made of corrugated cardboard are considered to be most suitable for the exportation of light-weight goods. However, the biggest problem with pallets made of normal corrugated cardboard is that the strength is reduced by water adhesion such as rain or moisture absorption.
This invention, which was made for the purpose of solving the above described problem, provides practical pallets made of corrugated cardboard, which can cope with rain or moisture, and water-resistant corrugated cardboard as the material for such pallets.
The water-resistant corrugated cardboard of this invention, which was created in order to solve the aforementioned problem, is characterized by water-resistant paper that is used for corrugated paperboard and flat paperboard, which are glued together with cornstarch glue containing 7 to 10 percent by weight modified ketone resin.
First of all, water-resistant paper is used for corrugated paperboard and flat paperboard, which are the main materials for the water-resistant, corrugated cardboard of this invention. Though various types of water-resistant papers are on the market, the one whose size xe2x80x9cCobb sizexe2x80x9d is larger than that of the conventional corrugated cardboard paper is desirable for use in corrugated cardboard. For this purpose, the strength of the paper itself (initial strength) increases yet its strength is less reduced by rain. Needless to say, the amount of moisture absorption is so little that the strength is not reduced if it is used or kept in the environment that is high in humidity.
Next, for the glue to join the corrugated paperboard and the flat paperboard, one having water-resistance and/or humidity-resistance is used. However, a large amount of glue is needed to manufacture corrugated cardboard, which must remain cost-competitive by comparison with the wooden pallet. There are plenty of types of glues, many of which are water-resistant, but there has been no such kind of glue as to be cheap enough for corrugated cardboard. Thus, the inventor of this invention came up with the idea that the cornstarch glue presently used for corrugated cardboard could be used as the base and additive with a water-resistant element added to it, and therefore various experiments were repeatedly conducted. As a result, the inventor discovered that the modified ketone resin adds sufficient water-resistance to cornstarch glue while keeping the cost increase to a minimum. The suitable volume to be added is 7 to 10 percent by weight. If it is less than this, there will not be enough water resistance. If more volume is added, the liquidity of cornstarch glue becomes insufficient, causing difficulty in the cardboard manufacturing process.